Diabetes is a metabolic disorder which is rapidly emerging as a global health care problem that threatens to reach pandemic levels. The number of people with diabetes worldwide is expected to rise from 285 million in 2010 to 438 million by 2030. Diabetes results from deficiency in insulin because of impaired pancreatic β-cell function or from resistance to insulin in body, thus leading to abnormally high levels of blood glucose.
Diabetes which results from complete deficiency in insulin secretion is Type 1 diabetes and the diabetes due to resistance to insulin activity together with an inadequate insulin secretion is Type 2 diabetes. Type 2 diabetes (Non insulin dependent diabetes) accounts for 90-95% of all diabetes. An early defect in Type 2 diabetes mellitus is insulin resistance which is a state of reduced responsiveness to circulating concentrations of insulin and is often present years before clinical diagnosis of diabetes. A key component of the pathophysiology of Type 2 diabetes mellitus involves an impaired pancreatic β-cell function which eventually contributes to decreased insulin secretion in response to elevated plasma glucose. The β-cell compensates for insulin resistance by increasing the insulin secretion, eventually resulting in reduced β-cell mass. Consequently, blood glucose levels stay at abnormally high levels (hyperglycemia).
Hyperglycemia is central to both the vascular consequences of diabetes and the progressive nature of the disease itself. Chronic hyperglycemia leads to decrease in insulin secretion and further to decrease in insulin sensitivity. As a result, the blood glucose concentration is increased, leading to diabetes, which is self-exacerbated. Chronic hyperglycemia has been shown to result in higher protein glycation, cell apoptosis and increased oxidative stress; leading to complications such as cardiovascular disease, stroke, nephropathy, retinopathy (leading to visual impairment or blindness), neuropathy, hypertension, dyslipidemia, premature atherosclerosis, diabetic foot ulcer and obesity. So, when a person suffers from diabetes, it becomes important to control the blood glucose level. Normalization of plasma glucose in Type 2 diabetes patients improves insulin action and may offset the development of beta cell failure and diabetic complications in the advanced stages of the disease.
Diabetes is basically treated by diet and exercise therapies. However, when sufficient relief is not obtained by these therapies, medicament is prescribed alongwith. Various anti-diabetic agents being currently used include biguanides (decrease glucose production in the liver and increase sensitivity to insulin), sulfonylureas and meglitinides (stimulate insulin production), α-glucosidase inhibitors (slow down starch absorption and glucose production) and thiazolidinediones (increase insulin sensitivity). These therapies have various side effects: biguanides cause lactic acidosis, sulfonylurea compounds cause significant hypoglycemia, α-glucosidase inhibitors cause abdominal bloating and diarrhea, and thiazolidinediones cause edema and weight gain. Recently introduced line of therapy includes inhibitors of dipeptidyl peptidase-IV (DPP-IV) enzyme, which may be useful in the treatment of diabetes, particularly in Type 2 diabetes. DPP-IV inhibitors lead to decrease in inactivation of incretins glucagon like peptide-1 (GLP-1) and gastric inhibitory peptide (GIP), thus leading to increased production of insulin by the pancreas in a glucose dependent manner. All of these therapies discussed, have an insulin dependent mechanism.
Another mechanism which offers insulin independent means of reducing glycemic levels, is the inhibition of sodium glucose co-transporters (SGLTs). In healthy individuals, almost 99% of the plasma glucose filtered in the kidneys is reabsorbed, thus leading to only less than 1% of the total filtered glucose being excreted in urine. Two types of SGLTs, SGLT-1 and SGLT-2, enable the kidneys to recover filtered glucose. SGLT-1 is a low capacity, high-affinity transporter expressed in the gut (small intestine epithelium), heart, and kidney (S3 segment of the renal proximal tubule), whereas SGLT-2 (a 672 amino acid protein containing 14 membrane-spanning segments), is a low affinity, high capacity glucose transporter, located mainly in the S1 segment of the proximal tubule of the kidney. SGLT-2 facilitates approximately 90% of glucose reabsorption and the rate of glucose filtration increases proportionally as the glycemic level increases. The inhibition of SGLT-2 should be highly selective, because non-selective inhibition leads to complications such as severe, sometimes fatal diarrhea, dehydration, peripheral insulin resistance, hypoglycemia in CNS and an impaired glucose uptake in the intestine.
Humans lacking a functional SGLT-2 gene appear to live normal lives, other than exhibiting copious glucose excretion with no adverse effects on carbohydrate metabolism. However, humans with SGLT-1 gene mutations are unable to transport glucose or galactose normally across the intestinal wall, resulting in condition known as glucose-galactose malabsorption syndrome.
Hence, competitive inhibition of SGLT-2, leading to renal excretion of glucose represents an attractive approach to normalize the high blood glucose associated with diabetes. Lower blood glucose levels would, in turn, lead to reduced rates of protein glycation, improved insulin sensitivity in liver and peripheral tissues, and improved cell function. As a consequence of progressive reduction in hepatic insulin resistance, the elevated hepatic glucose output which is characteristic of Type 2 diabetes would be expected to gradually diminish to normal values. In addition, excretion of glucose may reduce overall caloric load and lead to weight loss. Risk of hypoglycemia associated with SGLT-2 inhibition mechanism is low, because there is no interference with the normal counter regulatory mechanisms for glucose.
The first known non-selective SGLT-2 inhibitor was the natural product phlorizin (glucose, 1-[2-β-D-glucopyranosyloxy)-4,6-dihydroxyphenyl]-3-(4-hydroxyphenyl)-1-propanone). Subsequently, several other synthetic analogues were derived based on the structure of phlorizin. Optimisation of the scaffolds to achieve selective SGLT-2 inhibitors led to the discovery of several considerably different scaffolds.
C-glycoside derivatives have been disclosed, for example, in PCT publications WO2004013118, WO2005085265, WO2006008038, WO2006034489, WO2006037537, WO2006010557, WO2006089872, WO2006002912, WO2006054629, WO2006064033, WO2007136116, WO2007000445, WO2007093610, WO2008069327, WO2008020011, WO2008013321, WO2008013277, WO2008042688, WO2008122014, WO2008116195, WO2008042688, WO2009026537, WO2010147430, WO2010095768, WO2010023594, WO2010022313, WO2011051864, WO2011048148 and WO2012019496 U.S. patents U.S. Pat. Nos. 6,515,117B2, 6,936,590B2 and 7,202,350B2 and Japanese patent application JP2004359630.
The compounds shown below are the SGLT-2 inhibitors which have reached advanced stages of human clinical trials: Bristol-Myers Squibb's “Dapagliflozin” with Formula A, Mitsubishi Tanabe and Johnson & Johnson's “Canagliflozin” with Formula B, Lexicon's “Lx-4211” with Formula C, Boehringer Ingelheim and Eli Lilly's “Empagliflozin” with Formula D, Roche and Chugai's “Tofogliflozin” with Formula E, Taisho's “Luseogliflozin” with Formula F, Pfizer's “Ertugliflozin” with Formula G and Astellas and Kotobuki's “Ipragliflozin” with Formula H.

In spite of all these molecules in advanced stages of human clinical trials, there is still no drug available in the market as SGLT-2 inhibitor. Out of the potential candidates entering the clinical stages, many have been discontinued, emphasizing the unmet need. Thus there is an ongoing requirement to screen more scaffolds useful as SGLT-2 inhibitors that can have advantageous potency, stability, selectivity, better half-life, and/or better pharmacodynamic properties. In this regard, a novel class of SGLT-2 inhibitors is provided herein.